Equipment
The hammer mill
What is a hammer mill and why do modern cider mills use one?
In short
A hammer mill has a rotor carrying free-swinging steel hammers spinning at high speed inside a housing. Fruit fed in is struck repeatedly and pulverised against the housing and a breaker plate, then passes out through a perforated screen whose hole size sets the maximum particle size.
It is the standard mill in fruit juice processing and in most commercial cider plants, because it is fast, continuous, self-clearing and gives a consistent pomace regardless of fruit condition.
The pomace it makes is much finer than a scratter’s, which raises potential juice yield but makes the pomace harder to drain — so a hammer mill is normally paired with a press that can handle a fine mash, and often with enzyme treatment.
How it works
The rotor is a shaft carrying discs, and pinned between the discs are flat steel hammers free to swing outward. At operating speed centrifugal force holds the hammers rigid, but they can fold back if they strike something they cannot break — which is what protects the machine from a stone or a bolt in the fruit. Apples entering the chamber are hit, thrown against the wall, hit again, and reduced until the fragments are small enough to pass the screen.
Screen aperture is the main setting. A coarse screen gives a pomace closer to scratter output; a fine screen gives something approaching a purée. Rotor speed, hammer condition and feed rate all shift the result, and a worn hammer set will quietly coarsen the grind over a season.
Because the mill is continuous and self-emptying, it sits naturally in a line: wash, sort, elevator, mill, mash pump, press. That integration, more than the milling itself, is why it dominates at scale.
Consequences for the juice
Fine milling raises the theoretical yield because more cells are ruptured, and it raises phenolic extraction because vastly more cell wall surface is exposed to the liquid phase. It also releases more pectin and more colloidal material, which is why hammer-milled mash is usually treated with pectinase before or during pressing in commercial practice — untreated fine mash can be almost unpressable, forming a slick, closed cake that seals against its own liquid.
Oxidation is rapid. A hammer mill aerates violently and produces enormous surface area at once, so polyphenol oxidase activity is intense in the seconds and minutes after milling. Plants that want a pale, fresh-tasting juice sulphite or gas the mash immediately, or pull the mill outlet under a blanket; plants making a traditional-tasting cider may simply let it happen.
The other consequence is solids. Fine milling puts more fine particulate into the juice, so a hammer-milled press run typically needs more settling, more enzyme or more centrifugation before fermentation than a scratter run does.
What a hammer mill is not good for
A fine mash will bring a rack and cloth press to a halt: the cheese seals, pressure builds without flow, and cloths burst. Small makers who buy a hammer mill on the strength of its throughput and then try to press in a basket press frequently discover this the hard way. If the press is a traditional one, the mill should be a scratter or the hammer mill should be fitted with the coarsest available screen.
It is also unsuited to fruit that must be handled gently for a specific reason — keeving, for instance, depends on an intact pectin fraction and on a mash chemistry that heavy shearing and rapid oxidation disturb. Traditional keeved cider production uses gentler milling and a long, cool maceration for that reason.
Wear, noise and safety
Also answered on this page
Questions this page covers, so you can tell at a glance whether it is the one you want.
- Is a hammer mill better than a scratter?
- Why does hammer-milled pomace not press?
- What screen size should a cider hammer mill use?
Related
What people ask next
Questions readers ask about the things this page mentions. Each one goes to the section that answers it rather than to a page written to receive the question.
- How are apples milled for cider
- What does pectin do in cider — Pectin is the structural polysaccharide that holds fruit cells together. In juice it holds haze in suspension, and it is the molecule keeving depends on: strip its methyl groups and it will gel with calcium and float the nutrients out of the juice.
- What is keeving — Keeving is a technique for starving a ferment of nitrogen so that it stops before all the sugar is gone, leaving a naturally sweet cider. Pectin is made to gel and float as a brown cap, carrying nutrients and yeast out of the juice with it.
- Why add pectic enzyme to cider — Pectic enzyme breaks down the pectin that holds a haze in suspension and makes juice hard to press, so the cider clears and the yield rises. It must not be used where a keeve is intended, because keeving depends on the pectin staying intact.
- Why does apple juice go brown when pressed — Polyphenol oxidase in the fruit reacts phenolics with oxygen the moment cells are broken, turning the juice brown. In cider making this is sometimes prevented with sulphite and sometimes encouraged, because it also drops harsh tannin out of solution.
- What is a belt press
Sources
What this page rests on. Where a source is marked as registered rather than read, CiderHQ is recording that the body is authoritative on the subject without claiming to have worked through the document itself. See our evidence policy for what each state means.
Cider and perry production technical training material
Peter Mitchell / Cider and Perry Academy · reference work · registered as competent for this subject
Searched again on 2026-08-25 and it remains the one printed source here that a bibliographic check cannot fix, because it is not a published work with an edition. It is course material issued to participants of a training programme, so there is no catalogue record to verify, no ISBN, and no lawful public copy. Its state stays `registered` for that reason rather than through inattention.
Hochschule Geisenheim University — beverage technology
Hochschule Geisenheim · university · retrieved 2026-08-24
German beverage-technology research covering apple wine and fruit juice processing, including the enzymology of clarification.
The New Cider Maker’s Handbook: A Comprehensive Guide for Craft Producers
Claude Jolicoeur, Chelsea Green Publishing, 2013. ISBN 9781603584739 · reference work · bibliographic record verified, not opened 2026-08-25
Bibliographic record verified on 2026-08-25 against the Open Library union catalogue: Chelsea Green Publishing, 2013, ISBN 9781603584739, one edition recorded. That establishes the citation points at a real book in a stated edition, which is what a citation needs and is all it establishes. No copy was opened and nothing is quoted from it. The book itself is in print and not digitised in any open collection; where CiderHQ needs a figure from this territory it uses an accessible research source instead and says so.
Where to go next
- Cider making equipment — The rest of the equipment material, grouped by what each piece is for.
- How cider is made — The methods this equipment exists to carry out.
- Troubleshooting — The faults that are traced back to equipment and to cleaning.